1) A BLOCK OF "SE'OR" DESIGNATED AS A CHAIR
QUESTION: Abaye quotes a Beraisa in Pesachim (45b) that says that a large block of Se'or (heavily leavened dough) that one designated as a seat may be kept in one's home on Pesach, because it is now considered a utensil and not a food of Chametz. Abaye adds that even though an ordinary chair becomes Tamei mid'Oraisa with Tum'as Moshav Zav when a Zav sits on it, this block of Se'or becomes Tamei only mid'Rabanan. Abaye's proof is that if it would become Tamei mid'Oraisa, then it would be a case of a food becoming Tamei with a Tum'ah Chamurah, which is not possible.
TOSFOS (DH Tum'asah) asks that if, mid'Oraisa, the block of Se'or is not considered a chair but rather it still has the status of a food, then it should also retain its status of Chametz and be forbidden to remain in one's home on Pesach!
ANSWER: The TOSFOS HA'ROSH answers that with regard to the prohibitions of Bal Yera'eh and Bal Yimatzei, Bitul alone suffices to permit one to keep Chametz in his home. Therefore, designating the Se'or as a chair is considered sufficient Bitul with regard to Bal Yera'eh and Bal Yimatzei, even though it does not suffice to make the Se'or into a chair mid'Oraisa with regard to Tum'as Moshav Zav.
2) A LIMB OR FLESH DANGLING FROM A PERSON
OPINIONS: In the Mishnah, Rebbi Meir states that a limb or flesh that dangles from a living person is Tahor. If the person dies, then the dangling flesh remains Tahor, and the dangling limb becomes Tamei only as Ever Min ha'Chai (a limb that was detached from a living person), but not as Ever Min ha'Mes. Rebbi Shimon argues and says that the limb remains Tahor.
What is the basis of the argument between Rebbi Meir and Rebbi Shimon?
(a) RASHI (DH k'Zayis Basar) and TOSFOS (DH Bein Tana Kama) explain that Rebbi Meir maintains that there is only one difference between an Ever Min ha'Chai and an Ever Min ha'Mes, although what exactly that difference is remains unclear. There is an opinion (that of Rebbi Eliezer, as quoted by the Gemara here) that a k'Zayis of flesh of a limb that fell off of a living person is Tamei, just as the limb itself is Tamei. This opinion is lenient with regard to a piece of bone the size of a barley grain that fell off the same limb, and maintains that the bone is Tahor. There is another opinion (that of Rebbi Nechunya) that rules the opposite: the k'Zayis of flesh that falls off of a limb is Tahor, while the bone that falls off the limb is Tamei.
Accordingly, Rebbi Meir's final statement in the Mishnah -- that a limb is Tamei only because of Ever Min ha'Chai and not because of Ever Min ha'Mes -- can mean one of two things. It can mean either that a k'Zayis of flesh that falls off an Ever Min ha'Chai is Tamei, but not a bone the size of a barley grain, or that a bone the size of a barley grain is Tamei, but not a k'Zayis of flesh. This is in contrast to an Ever Min ha'Mes, where both a k'Zayis of flesh and a bone the size of a barley grain that fall are Tamei. Rebbi Shimon argues that in both of these cases, the object that falls off is Tahor when it comes from an Ever Min ha'Chai, as opposed to when it falls from an Ever Min ha'Mes (in which case Rebbi Shimon agrees with Rebbi Meir that in both cases the object is Tamei).
(b) The RAMBAM (in Perush ha'Mishnayos) and the BARTENURA explain that Rebbi Meir maintains that in both the case of flesh and the case of a bone, the object is Tahor when it falls off an Ever Min ha'Chai. Only when it falls off an Ever Min ha'Mes is it Tamei. Rebbi Shimon maintains that the Halachah in all of the cases (a k'Zayis of flesh or a bone the size of a barley grain that fell from an Ever Min ha'Chai or from an Ever Min ha'Mes), the object is Tahor.
The RASHASH questions the opinion of the Rambam and Bartenura. No such argument appears anywhere else in the Gemara. Moreover, he asks, why would Rebbi Shimon say that a k'Zayis of flesh or a bone the size of a barley grain that came from the limb of a deceased person is different from such an object that came from the body of a dead person? In both cases, it comes from something that is Tamei with Tum'as Mes! It appears that his question assumes that Ever Min ha'Chai is more lenient, since the person himself is still alive and indeed may be Tahor. His limb is Tamei only because the Gemara (see Nazir 53b) derives from the verse that a limb that falls off a living person is Tamei, but there is no reason to extend this Halachah to small parts which become detached from his limb.
The TOSFOS YOM TOV seems to address the question of the Rashash. He writes that one should not be perplexed by the explanation of the Rambam and Bartenura. The Mishnah in Eduyos (6:2) quotes Rebbi Eliezer who maintains that an Ever Min ha'Mes that is smaller than a k'Zayis is not Tamei, even though an Ever Min ha'Chai that is smaller than a k'Zayis is Tamei. Rebbi Eliezer apparently maintains that there is a stringency with regard to an Ever Min ha'Chai. This is not evident according to any opinion in the Mishnah here. The Tosfos Yom Tov apparently means that the Rashash's logic that something that comes from a Mes is always Tamei is not universally accepted, because even a whole limb from a Mes can be Tahor if it is not the size of a k'Zayis.
However, the LEV ARYEH rejects the Tosfos Yom Tov's logic. Rebbi Eliezer says that an Ever Min ha'Mes is not Tamei only because the Ever is smaller than a k'Zayis. Just as flesh of a dead person which is smaller than a k'Zayis is not Tamei, a limb from a Mes which is smaller than a k'Zayis is not Tamei. Only with regard to an Ever Min ha'Chai is there a Halachah that something is Tamei (even if it is smaller than a k'Zayis) solely because it is a limb in itself. Therefore, Rebbi Shimon's statement in the Mishnah here (according to the Rambam) that a k'Zayis of meat from the limb of a dead person is Tahor remains difficult. (See Lev Aryeh at length.) (Y. MONTROSE)